Various elastic composites have been formed by bonding an elastic polymer layer in the form of a film, foam, nonwoven web or parallel strands, to one or more nonwoven facing layers. A “stretch bonded laminate” (“SBL”) is any laminate in which an elastic layer is bonded to one or more facing layers while the elastic layer is stretched. When the elastic layer is subsequently relaxed, gathers form in the facing layer(s). Stretch-bonded laminates are described, for instance, in U.S. Pat. No. 5,952,952 to Shawver et al., U.S. Pat. No. 6,387,471 to Taylor et al., and U.S. Pat. No. 6,323,389 to Thomas et al., which are incorporated herein by reference. A “neck-bonded laminate” (“NBL”) is any laminate where an elastic layer is bonded to one or two non-elastic facing layers while the elastic layer is relaxed and the facing layer(s) are extended or necked to reduce their dimensions in the direction orthogonal to the extension. Neck-bonded laminates have cross-directional stretch and recovery properties. Neck-bonded laminates are described, for instance, in U.S. Pat. No. 5,853,881 to Estey et al., U.S. Pat. No. 4,965,122 to Morman, and U.S. Pat. No. 6,001,460 to Morman et al., and U.S. Pat. No. 5,789,065 to Haffner et al., which are incorporated herein by reference. A “neck-stretch bonded laminate” (“NSBL”) is any laminate where an elastic layer is bonded to one or two facing layers while the elastic layer is stretched, and the facing layer(s) are extended in the same direction to cause necking in the direction orthogonal to the extension. Thus, a NSBL has features common to both a SBL and a NBL.
Various thermoplastic elastomers are known for use in the elastic layer, including without limitation styrenic block copolymers. For instance, U.S. Pat. No. 6,323,389 to Thomas et al. discloses the use of block copolymers having the general formula A-B-A′ or A-B, wherein A and A′ are each a thermoplastic polymer end block which contains a styrenic moiety such as a poly(vinylarene) and B is an elastomeric polymer midblock such as a conjugated diene or a lower alkene polymer. The A and A′ blocks may be formed of the same or different polymer segments. Tetrablock copolymers having the formula A-B-A-B are also disclosed, where A is a thermoplastic polymer block as described above, and each B is an isoprene segment hydrogenated substantially to a poly(ethylene-propylene) segment.
Elastic laminates are typically the most expensive component in personal care products such as diapers, diaper pants, adult incontinence garments, feminine hygiene products and the like. Important properties of elastic laminates include providing sufficient elastic tension at various degrees of elongation during use, and providing sufficient recovery upon stress relaxation (creep resistance).
There is a need or desire for elastic laminates which achieve these objectives, at reduced expense, for instance by requiring lower amounts of elastic polymer material, and for improved elastic polymers which facilitate these objectives.